The present invention relates to the field of materials research, and more in particular, to simultaneous creation of numerous diverse compounds in one step for further analysis, testing, and evaluating of different properties of these compounds as the entire multi-component system created on a single substrate.
The present invention further relates to a combinatorial synthesis technique which is based on pulsed laser deposition or other deposition techniques based on ablation due to an energetic beam such as a pulsed electron beam, in combination with a continuous composition spread technique resulting in a deposition film formed on a substrate having a continuously varying composition of a plurality of selected ingredient materials.
Further, the present invention relates to a combinatorial synthesis system and method in which a plurality of targets are ablated in a predetermined sequence by an energetic beam, such as a laser beam or a pulsed electron beam, such that the ejected materials reach a substrate at predefined locations thereon and form a plurality of deposition centers on the substrate. Each deposition center is surrounded by a distributed deposition area with a lower concentration of the material than at the corresponding deposition center. The distributed deposition areas of all deposition centers overlap each other forming a deposition film on the surface of the substrate having a continuously varying composition of the ingredient materials of the targets.
The present invention still further relates to a combinatorial synthesis system in which each target during the time of exposure to energetic pulses, such as laser pulses, is aligned with a corresponding deposition center on the substrate by means of a control mechanism which controls a mutual disposition between the energetic beam, targets, and the substrate in the following manner:
A. Either the energetic beam is maintained immovable, and the targets are displaced (rotated on the target carousel) to bring a target into operational engagement with the energetic beam, additionally, the substrate is rotated to align the predefined deposition center with a corresponding target; or
B. The substrate and/or the targets are maintained stationary and the energetic beam is steered from target to target which may or may not be repositioned during the deposition. The energetic beam also may be controlled to scan over the surface of a particular target to further control the composition deposited on the substrate.
A deposition film created in this manner on the surface of the substrate having a continuously varying composition of the ingredient materials may then be further analyzed, tested, and evaluated in searching for a compound having specific physical, electrical, optical, etc., properties.
Combinatorial chemistry was introduced in the mid 1980s as a method by which drug researchers could quickly make and evaluate a large number of products and check the biological activity. Combinatorial chemistry has attracted intense interest in the scientific community. Combinatorial chemistry is an approach in which a large number of compounds are synthesized without thorough predictions of likely reactions or the properties of the resulting substances. In its basic parallel synthesis form, combinatorial chemistry uses an array of tiny wells in a plastic sheet filled row by row with chemicals A1, A2, A3 . . . , and column by column with reacting chemicals B1, B2, B3 . . . Each well""s reaction product is analyzed with a generalized test of biological activity and those giving positive results are pursued.
More recently, the combinatorial approach has been applied to thin film materials synthesis with the expectations of developing new luminescent materials, magnetoresistive compounds, dielectric and ferroelectric materials, catalysts, polymers, and high-Tc superconductors. In this approach, an array of thin film squares are deposited on a single substrate, each with a slightly different composition. Presently, researchers are applying combinatorial chemistry techniques to optical, electronic, superconductive and magnetic materials for differences in bulk compositions, layer compositions, layer thicknesses, composition changes with respect to depth, and magnetic properties. Present day material science examines the small compositional differences that may induce profound property changes.
There are several techniques in the combinatorial chemistry used to create a plurality of different compounds on a single substrate for further analysis, testing and evaluation. In the discrete combinatorial synthesis (DCS) approach, a series of masks is used to deposit separate layers of the ingredient materials. As shown in FIGS. 1A-1D, different materials A, B, C, and D are deposited in sequence through masks (not shown) followed by a high temperature anneal to promote reaction of the components. This forms different compounds of the ingredient materials, as shown in FIG. 1E. Large numbers of materials may be synthesized in a single run. The masks have to be brought in close contact with the substrate in order to permit the required spatial resolution. In many situations this requires the deposition to take place at room temperature since handling of complex delicate masks at elevated temperatures poses a difficulty.
More fundamentally, discrete combinatorial synthesis techniques require a high temperature anneal after deposition of the precursor layers in order to promote intermixing of the components and is thus not suitable for the exploration of low temperature processed materials.
A high temperature DCS system has been developed by Pascal Corporation, Ltd. (Japan). Disadvantageously, this system allows a very limited number of compositions to be generated per run at a relatively high cost. Clearly, the elevated cost of such systems in combination with the limited number of compositions generated per run prohibit commercial widespread use.
Another discrete combinatorial synthesis system is described in U.S. Pat. No. 5,985,356 in which a substrate having an array of diverse materials thereon is generally prepared by delivering components of materials to predefined regions on a substrate. Simultaneously the components are reacted to form at least two materials. In this system, eight RF magnetron sputtering guns each of which contains a reactant component of interest are located above a disk containing eight masking patterns as well as eight film thickness monitors.
The magnetron sputtering guns, as well as the disk, are fixed in this system. The substrate is coupled to a substrate manipulator which is capable of linear and rotational motion and which engages the substrate with a particular mask of interest so that the substrate is in contact with the mask when the sputtering is initiated. Combinations of the eight components are generated on the substrate by the sequential deposition of each component through its respective mask.
To overcome deficiencies of the described combinatorial synthesis techniques, the continuous composition spread (CCS) technique has been introduced in 1970 by J. T. Hanak. In this type of proposed system films are deposited by co-sputtering from a disk-shaped target consisting of 120xc2x0 sectors of three different materials. In 1998, R. B. Van Dover, et al. introduced a CCS technique by reactive co-sputtering using planar magnetron sputter guns arranged at 90xc2x0 intervals around a rectangular substrate. Zr, Ti and Sn guns are typically run at 150 watt, 75 watt, and 20 watt of radio frequency power, respectively, in order to provide the desired Zr/Ti/Sn composition at the substrate midpoint. The deposited film constitutes a single film with a ternary composition spread, the critical properties of which are evaluated as a function of position.
The composition was inferred as a function of position using Rutherford backscattering spectroscopy together with independent calibration runs allowing a mapping of the xe2x80x9cuseful figure of meritxe2x80x9d (FOM) data onto a conventional ternary phase diagram. The same CCS approach was used in 1999 for the discovery of an amorphous high-K dielectric.
As an alternative approach, a mask based post anneal approach to continuous composition spread technique has been proposed by Kurt J. Lesker Company, in which continuous xe2x80x9cwedgesxe2x80x9d of each component are deposited using a moving shutter in a sputter system. The tool is commercially available under the name xe2x80x9cCMSxe2x80x9d.
Despite the advantages of the conventional continuous composition spread technique over the discrete combinatorial synthesis approach such a technique requires large sputter targets. Thus, conventional systems fail to enjoy the benefits of pulsed laser deposition technique allowing for use of small targets. It is known to those skilled in the art that pulsed laser deposition is a proven prototyping method with advantages over sputtering, evaporation, or CVD (chemical vapor deposition) approaches. In the pulsed laser deposition technique, a laser beam impinges on the surface of a target formed of a predetermined material composition and ablates the target thus ejecting the particulates of the material of the target towards a substrate where the material is deposited.
In view of the disadvantages of discrete combinatorial synthesis and sputter based continuous composition spread technique it is advantageous to provide a combinatorial synthesis approach which enjoys the positive features of the continuous composition spread technique in combination with pulsed laser deposition which allows deposition of materials under similar conditions with a similar growth rate as well as permitting use with small targets which are sufficient for most applications and thus available for virtually all desirable material.
It is therefore an object of the present invention to provide a combinatorial synthesis technique based on pulsed laser deposition technology or other deposition approach based on ablation or sputtering due to an energetic beam, such as a pulsed electron beam, and continuous composition spread techniques for creating a deposition film having a continuously varying composition of ingredient materials and allows an unlimited number of materials to be deposited on a substrate while removing the disadvantage of contamination due to contact with a mask.
It is another object of the present invention to provide a combinatorial synthesis technique which permits creation of a high number of different compounds in a single run in a highly cost effective manner.
It is a still further object of the present invention to provide a combinatorial synthesis system in which a plurality of targets are brought in direct contact with an energetic beam in a predetermined sequence in order that the surface of each target is ablated and the material particles are ejected towards the substrate where they are deposited at a predefined deposition center surrounded by a distributed deposition area. The distributed deposition areas of all deposition centers on the substrate are generally in overlapping relation so that a final deposition film created on the surface of the substrate constitutes an uninterrupted spread with a continuously varying composition of the materials of the targets. The deposition film is further analyzed, tested and evaluated on the basis of measurements of the thickness of the entire multi-component film at a few selected points that is sufficient to determine the elemental distribution.
It is a further object of the present invention to provide a combinatorial synthesis system in which either the energetic beam is maintained immovable while the targets and the substrate are displaced from their original position for inter-alignment and inter-engagement between all required parts of the system, or the energetic beam steers from one target to another and is capable of scanning over the surface of each particular target, and where the position of the targets and/or substrate additionally may be changed during the deposition.
In accordance with the teaching of the present invention, the combinatorial synthesis system includes a plurality of targets supported on a target carousel or other target positioning equipment and arranged thereon in a predetermined relationship therebetween. Each target is formed of a respective material which serves as an ingredient material for creation of a plurality of ingredient materials compound. A substrate is displaced from the targets a predetermined distance. A plurality of deposition centers are defined on the substrate in correspondence to the targets.
An energetic beam such as a laser beam, a pulsed electron beam, etc. is directed towards one of the targets for ablating the surface of the target and ejecting particulates of the xe2x80x9cingredientxe2x80x9d material of the target towards the substrate. The ejected particulates are deposited at the corresponding deposition centers and at a distributed deposition area surrounding each deposition center. The distributed deposition areas of the deposition centers on the substrate overlap each with the other, thus forming a continuously spread deposition film on the surface of the substrate having a continuously varying composition of the ingredient materials.
It is essential that the combinatorial synthesis system of the present invention include a control mechanism adapted to control mutual disposition between the energetic beam, targets and the substrate and in particular provides coordination between the targets and corresponding deposition centers. The control mechanism may maintain the energetic beam immovable while rotating the target carousel to bring the targets in contact with the stationary energetic beam sequentially, and rotate the substrate in order to align the deposition center with the corresponding target. Alternatively, the substrate and/or the targets are maintained stationary while the control mechanism steers the energetic beam from one target to another in a predetermined sequence. It is important that the energetic beam can be steered not only from one target to another, but that also the energetic beam is capable of scanning the surface of each target.
In the system using the immovable energetic beam, the rotation of the target carousel and alignment of the substrate with the targets is performed between the energetic pulses. In the system using a steered energetic beam, the focusing of the energetic beam on a required target is also performed between the pulse generation. For each target, the number of laser or electron beam pulses or the duration of exposure to an ion beam is determined by the control mechanism.
The targets may be formed as disk-shaped targets spaced each from the other on the target carousel or they may be formed as wedge-shaped targets radially disposed on the common disk-shaped support on which they are angularly spaced each from the other.
Preferably, the substrate is positioned in direct contact with the heater with all elements of the system received in the vacuum chamber.
The substrate can linearly move towards and away from the targets to provide a flexibility of use in depositing the ingredient materials onto the substrate surface.
Viewing in another aspect thereof, the present invention is a combinatorial synthesis method which includes the steps of directing an energetic beam towards one of a plurality of targets and varying disposition in a predetermined sequence between the energetic beam and the target (either with the immovable energetic beam or with steerable energetic beam).
It is essential that the composition deposited on the substrate varies continuously between different regions of the substrate and can be further analyzed by determining the compositional map across the sample without having to perform sophisticated chemical analysis. Measurement of the thickness of the entire multi-component film at a few selected points has been found to be sufficient in determining the elemental distribution based on a few basic assumptions that can be verified periodically on test wafers.
These and other novel features and advantages of this invention will be fully understood from the following detailed description of the accompanying drawings.